My two cents: Skip the kid peeing....it's a copyright violation of Calvin as in "Calvin and Hobbs" Mr. Watterson, the creator, has never sued anyone for it (too much hassle), but it's bad karma nonetheless to violate a copyright. The other ideas are funny and creative IMO.

FYI: here's the reference for the peeing calvin from wikipedia:

""Except for the books, two 16-month calendars (1988–1989 and 1989–1990), Teaching with Calvin and Hobbes,[6] and one T-shirt for a traveling art exhibit on comics, virtually all Calvin and Hobbes merchandise is unauthorized. One of the widely circulated counterfeit items is a series of window decals depicting Calvin grinning wickedly as he urinates on various companies' logos. As Watterson pointed out during the notes of one of the collection books, the original image was of Calvin filling up a water balloon from a faucet. After threat of a lawsuit alleging infringement of copyright and trademark, some of the sticker makers replaced Calvin with a different boy, while other makers ignored the issue.[citation needed] Watterson wryly commented, "I clearly miscalculated how popular it would be to show Calvin urinating on a Ford logo."[19] Some legitimate special items were produced, such as promotional packages to sell the strip to newspapers, but these were never sold outright.""

Here's the original picture: